Thermionic device



Filed Jan. 22, 1932 INVENTO! NIC EL-MOLYBDENUM I ON-A LOY ATTORNEYS. I

Patented June 19, 1934 James A. Holladay, Douglaston, N. Y., assignor toKemet laboratories Company, Inc., a corporation of New York ApplicationJanuary 22,

4Claims.

The invention relates to metallic parts of thermionic and similardevices. It is directed especially to grid electrodes of thermionicvalves or radio tubes, but is applicable to other metallic 6 parts ofradio tubes and thermionic devices generally. The chief object of theinvention is to provide parts for such devices fabricated from a groupof alloys having the mechanical, chemical and electrical propertieswhich render them adaptable to such application.

One type of thermionic devices to which'the invention is applicable isillustrated in the sole figure of the accompanying drawing, in'which areshown an envelope 10 containing elements consisting of an electronemitting cathode 11, an anode 13, a grid 12 located between the cathodeand anode, a hook-wire 14 for supporting the cathode, and supportingwires 15 for supporting the cathode, anode, and grid within the envelope10.

In the present state of the art it cannot be predicted in advance ofactual trial whether or not a hitherto untried metal or alloy will besuitable for the manufacture of the metallic elements of radio tubes;this is especially true of metals to be used for grid electrodes. Allradio tube elements must be non-corroding and relatively non-tarnishingunder the conditions of manufacture, storage and use, relatively freefrom occluded gas, and possess at least a moderate degree of ductility.Grid wires must have, in addition to these properties, a high meltingpoint, and a large number of special characteristics required for easymanipulation in manufacture, which include: springiness or resilience,stiffness, a high tensile strength and high elongation under tensiletest, and uniformity of properties throughout the length of the wire.The wires must not deform when used in a tube. Furthermore, thecompleted tube elements must 40 have suitable electrical characteristicsand a long life in use.

I have discovered that alloys which comprise chiefly nickel, molybdenumand iron within certain limits of composition, may successfully be 5fabricated into grid electrodes and other operating elements of radiotubes and similar devices,

and that elements so fabricated have the mechanical, chemical andelectrical properties essential for satisfactory performance in suchdevices.

The alloys included in my invention comprise those which contain atleast 40% of nickel, from about 15% to about 40% of molybdenum, and fromabout 10% to about 30% of iron. The presence of vanadium in amounts ofabout 0.3% is 1932, semiar d. 588.244

beneficial, but not essential. Small amounts of carbon and metals suchas manganese and silicon may also be present, but large amounts of thesematerials are undesirable; For instance, up to about 2.5% of manganeseimproves the workability of the alloy, but the manganese content shouldnot exceed about 4%. The silicon content should preferably be belowabout 0.5%, and the carbon content below about 0.3%. Such impurities assulfur and phosphorus are detrimental, and should be present only invery low quantities. Cobalt may be substituted in whole or in part forthe nickel, and tungsten may be substituted at least in part for themolybdenum.

Alloys, of the above description possess the 7 requisite properties forfabrication into and use as various structural parts of electronictubes, of both the vacuum and'the gas-filled types, and the tubesproduced by assembly of these structural parts function in asatisfactory manner chemically, electrically and mechanically.

The following description of one application of my invention, to radiotube grid electrodes, serves as an example. An alloy havingapproximately the following composition: 58% of nickel, 20% 30 ofmolybdenum, 2.25% of manganese, 0.30% of vanadium, 0.20% of silicon,0.10% of carbon, and the remainder iron was drawn down to wire having adiameter of about 0.005 inches. Samples of this wire were annealed atseveral different 35 temperatures between about 900 C. and 1200 C. Thisheat treatment was found to provide a control of the stretch of the wirebetween about 5% and 30%, with a corresponding range of yield pointsbetween about 140,000 and 100,000 pounds per square inch, and ofultimate tensile strengths between about 170,000 and 115,000 pounds persquare inch. The higher the annealing temperature, in general, thehigher the resulting stretch of the wire will be, and the lower theyield point and ultimate strength. The above stretch figures wereobtained on ten-inch samples of wire stretched to rupture. The stretchfigures may be taken as indicative in a qualitative way of theelongation of the metal under standard elongation test conditions.

The heat treated wire samples were than made into radio tube grids.About five hundred grids were made during this experiment, includingvarious types of flat, rectangular and round structures. During themanufacture of these grids it was observed that the wire was strong,stiff, had a good surface finish, handled well on the automaticmachinery, and'responded properly to the various operations such aswinding, swaging, 11o

'(about 1330 C.) and relative cheapness. Furthermore, the alloy has ahigh tensile strength for a given elongation, and this ratio iscontrollable not only by change inthe composition of the alloy, but alsoby subjecting the alloy to varying degrees of cold working. Whiledrawing wire for grids, for example, a severe cold working by rapidreduction of cross sectiontends to give a brittle material with a hightensile strength. A more gradual reduction in cross section yields aless brittle material with a lower tensile strength. Intermediateannealing during the drawing lessens the brittleness of the flnalmaterial, and lowers the tensile strength considerably. I prefer to drawthe wire by rapidreductions of area and at the most only slightintermediate annealing, and to impart the necessary stretchcharacteristics to the finished wire by one anneal after drawing iscompleted. This procedure gives a satisfactory wire for grid-wire. It ispossible to control the elongation within close limits over a wide rangeby varying the annealing conditions as explained above.

It is to be emphasized that the particular properties most desired ingrid wire are different for different types of grids, and vary alsoaccording to the methods and machines used in fabrication. For example,different practices in such operations as swaging, stripping, annealingand stretching of the grids in process require correspondingly difierentcharacteristics in the grid materialfor successful manufacture. Probablythe greatest advantage in the alloys of the invention is the fact thatthey possess in addition to the peculiar set of properties required forgrid manufacture the ability to change their physical properties overwide ranges under suitable control of the mechanical treatment imposedupon them.

While the application of my invention to radio tube grid wires hasherein been stressed in the description and exampleait will beunderstood that a material whichwill meet the difficult requirements ofthis application will also meet the less difilcult requirements of manyother elements of electronic devices, such' for example as supportwires, core wire for certain coated filaments, filamenthook supportwires, plates and the like. I

I claim: v

. 1. A thermionic device comprising an envelope; elements consisting ofan electron emitting cathode, an anode, at least one grid electrodelocated between the cathode and anode, and means for supporting saidcathode, anode and grid electrodes within said envelope; at least one ofthe elements within said envelope being composed of an alloy having thecomposition of from about 15% to about 40% of molybdenum, from about 10%to about 30% of iron, andthe balance chiefly of nickel.

2. A grid electrode suitable for use in a thermionic valve whichcomprises an alloy having substantially the following composition: fromabout 15% ,to about 40% molybdenum, from about 10% to about 30% of iron,and the balance chiefly of nickel.

3. A grid electrode suitable for use in a thermionic valve whichcomprises an alloy having substantially the following composition: 20%of molybdenum, 58% of nickel, 2.25% of manganese, 0.30% ofvanadium,'0.20% of silicon, 0.10% of carbon, and the remaindersubstantially iron.

4. A grid electrode suitable for use in a thermionic valve whichcomprises an alloy having the following composition: about 15% to 40%molybdenum, about 10% to 30% iron, approximately 0.3%vanadium,-manganese in an amount not over about 2.5%, silicon in anamount not over about 0.5%, carbon in an amount not over about 0.3%, thebalance substantially all nickel; the nickel being present in an amountat least 40% of the alloy.

JAMES A. HOLLADAY.

